journal of palaeogeography 4 (2015) 384e412 HOSTED BY Available online at www.sciencedirect.com ScienceDirect journal homepage: http://www.journals.elsevier.com/journal-of- palaeogeography/ Lithofacies palaeogeography of the Carboniferous and Permian in the Qinshui Basin, Shanxi Province, China * Long-Yi Shao a, , Zhi-Yu Yang a, Xiao-Xu Shang a, Zheng-Hui Xiao a,b, Shuai Wang a, Wen-Long Zhang a,c, Ming-Quan Zheng a,d, Jing Lu a a State Key Laboratory of Coal Resources and Safe Mining, School of Geosciences and Surveying Engineering, China University of Mining and Technology (Beijing), Beijing 100083, China b Hunan Provincial Key Laboratory of Shale Gas Resource Utilization, Hunan University of Science and Technology, Xiangtan 411201, Hunan, China c No.105 Geological Brigade of Qinghai Administration of Coal Geology, Xining 810007, Qinghai, China d Fujian Institute of Geological Survey, Fuzhou 350013, Fujian, China article info abstract Article history: The Qinshui Basin in the southeastern Shanxi Province is an important area for coalbed Received 7 January 2015 methane (CBM) exploration and production in China, and recent exploration has revealed Accepted 9 June 2015 the presence of other unconventional types of gas such as shale gas and tight sandstone Available online 21 September 2015 gas. The reservoirs for these unconventional types of gas in this basin are mainly the coals, mudstones, and sandstones of the Carboniferous and Permian; the reservoir thicknesses Keywords: are controlled by the depositional environments and palaeogeography. This paper presents Palaeogeography the results of sedimentological investigations based on data from outcrop and borehole Shanxi Province sections, and basin-wide palaeogeographical maps of each formation were reconstructed Qinshui Basin on the basis of the contours of a variety of lithological parameters. The palaeogeographic Shanxi Formation units include the depositional environments of the fluvial channel, flood basin (lake), upper Taiyuan Formation delta plain, lower delta plain, delta front, lagoon, tidal flat, barrier bar, and carbonate Coal measure platform. Coalbed methane The Benxi and Taiyuan Formations are composed mainly of limestones, bauxitic Permian mudstones, siltstones, silty mudstones, sandstones, and economically exploitable coal Carboniferous seams, which were formed in delta, tidal flat, lagoon, and carbonate platform environ- ments. The Shanxi Formation consists of sandstones, siltstones, mudstones, and coals; during the deposition of the formation, the northern part of the Qinshui Basin was occu- pied mainly by an upper delta plain environment, while the central and southern parts were mainly occupied by a lower delta plain environment and the southeastern part by a delta front environment. Thick coal zones occur in the central and southern parts, where the main depositional environment was a lower delta plain. The thick coal zones of the Taiyuan Formation evidently occur in the sandstone-rich belts, located mainly in the lower * Corresponding author. E-mail address: [email protected] (L.-Y. Shao). Peer review under responsibility of China University of Petroleum (Beijing). http://dx.doi.org/10.1016/j.jop.2015.06.001 2095-3836/© 2015 The Authors. Production and hosting by Elsevier B.V. on behalf of China University of Petroleum (Beijing). This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). journal of palaeogeography 4 (2015) 384e412 385 delta plain environment in the northern part of the basin and the barrier bar environments in the southeastern part of the basin. In contrast, the thick coal zones of the Shanxi For- mation extend over the mudstone-rich belts, located in the areas of the lower delta plain environments of the central and southern parts of the Basin. The Xiashihezi, Shangshihezi, and Shiqianfeng Formations consist mainly of red mudstones with thick-interbedded sandstones. During the deposition of these formations, most areas of the basin were occupied by a fluvial channel, resulting in palaeogeographic units that include fluvial channel zones and flood basins. The fluvial channel deposits consist mainly of relatively-thick sandstones, which could have potential for exploration of tight sandstone gas. © 2015 The Authors. Production and hosting by Elsevier B.V. on behalf of China University of Petroleum (Beijing). This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/). that the coal measures (Benxi, Taiyuan, and Shanxi Forma- 1. Introduction tions) were formed within delta and tidal flat-lagoon depo- sitional systems (Cheng, 1992; IGE-CCMRI/SPCEC, 1987; Shao The Qinshui Basin in southeastern Shanxi Province, northern et al., 2007). However, studies focusing on the depositional China has become a hot spot for coalbed methane exploration controls of the distribution of the No. 3 and No. 15 coal seams, and production since the 1990s (Liu et al., 1998; Zhang and the targeted seams for methane extraction, are still scarce. Wang, 1999). The coalbed methane resource in this basin is Furthermore, the facies distribution of the overlying non-  12 3  12 3 estimated to be 3.28 10 m (CNACG, 1998) or 5.52 10 m marine strata (Xiashihezi, Shangshihezi, and Shiqianfeng (Zhang et al., 2002). Recent exploration has also confirmed Formations) is not fully analyzed and the depositional that this basin has great potential for shale gas and tight mechanisms of these siliciclastic successions are still not sandstone gas in its Carboniferous and Permian strata (Dai well understood. These aspects would influence the design and Qi, 1981; Gu et al., 2011; Qin et al., 2014; Shao et al., schemes of unconventional gas exploration and extraction in 2014). Because of this large amount of unconventional re- this basin. In addition, a basin-wide synthesis of palae- sources, the Qinshui Basin has attracted extensive coalbed ogeography and its evolution for these lithological forma- methane exploration and development from a variety of tions has not been provided, and the palaeogeographical authorities, including the China United Coalbed Methane Co. evolution and its controls on the facies distribution should be Ltd., China National Petroleum Corporation, and overseas of significance to unconventional gas exploration and pro- joint ventures, as well as some local coal mine administra- duction in this basin. tions such as the Jincheng Coal Industry Group Co. The From the 1970s to the 1980s, coal depositional models 3 highest coalbed methane production is 16,000 m /d per well, established for the Carboniferous coal measures in northern e 3 and the average is 2000 4000 m /d per well in this basin in England and Appalachian basins have been proven to be recent years. Exploration has confirmed that coalbed methane effective in coal exploration in these areas (Ferm and Staub, reservoirs in this basin are dominated by semi-anthracite and 1984; Fielding, 1984; Guion et al., 1995; Horne et al., 1978; anthracite with vitrinite reflectance between 2.2% and 4.5%, Marchioni et al., 1996). Although depositional environments with high permeability and high gas contents (Jin et al., 2008; and coal accumulation have been studied in parts of the Qin- Su et al., 2005). The shale gas resource assessment organized shui Basin, e.g., the Yangquan mine area and the Shouyang ' recently by the Ministry of Land and Resources of the People s mine area (Ge et al., 1985; Huang et al., 1989), a basin-wide  12 3 Republic of China has confirmed a reserve of 0.49 10 m , depositional model and lithofacies palaeogeography of the showing a great potential for shale gas exploration in this Carboniferous and Permian have not been studied, and this basin (Fang et al., 2013; Gu et al., 2011). should be of great significance to the exploration of coal, As an important energy resource basin, the Qinshui Basin coalbed methane, as well as tight sandstone gas. has been widely investigated for its geological characteris- In this paper, we focus on basin-wide palaeogeographical tics, including the structural geology, depositional environ- reconstruction of each formation of the Carboniferous and ments, coal accumulation, coal measures stratigraphy, and Permian, based on numerous selected data points including coalbed methane geology (Chen and Liu, 1998; Qin et al., 1997; outcrop sections and boreholes. Sun et al., 1998; Su et al., 2005; Wei et al., 2002; Ye et al., 2002). In particular, the depositional models of the coal measures (Benxi, Taiyuan and Shanxi Formations) in this basin have 2. Geological setting been extensively studied (Cheng, 1992; CNACG, 1997; Ge et al., 1985; Huang et al., 1989; IGE-CCMRI/SPCEC, 1987; The Qinshui Basin is located at the southeastern Shanxi Shao et al., 2007; Zhang et al., 2001). It is generally accepted Province, with geographical coordinates of N35 e38 and 386 journal of palaeogeography 4 (2015) 384e412 Fig. 1 e Division of the mining and exploration areas in the Qinshui Basin. IeShouyang area; IIeYangquan area; IIIeHeshuneZuoquan area; IVeTunliueZhangzi area; VeGaopingeFanzhuang area; VIeJincheng area; VIIeAnzeeQinshui area; VIIIeQinyuan area. Only some representative studied outcrops and boreholes are shown with names, while others only with the location. journal of palaeogeography 4 (2015) 384e412 387 Fig. 2 e Stratigraphic subdivision and sub-correlation of the Carboniferous and Permian strata in the Qinshui Basin (modified after Cheng, 1992 and CNACG, 1997). 388 journal of palaeogeography